import React, { Component } from 'react'

export default class Count extends Component {
    state = {
        count : 0                                                                                                                                                                                                                         
    }
    increment = ()=> {
        const {value} = this.selectNumber
        const {count} = this.state
        // *1 强制类型转换
        this.setState({count: count + value*1})
    }
    // 减法
    decrement = ()=> {
        const {value} = this.selectNumber
        const {count} = this.state

        this.setState({count: count - value*1})

    }
    incrementIfOdd = ()=> {
        const {value} = this.selectNumber
        const {count} = this.state
        if(count % 2 !== 0) {
        this.setState({count: count + value*1})}

    }
    // 异步加
    incrementAsync = ()=> {
        const {value} = this.selectNumber
        const {count} = this.state
        setTimeout(()=> {
            this.setState({count: count + value*1})
        }, 1000)
    }
    render() {
        return (
            <div>
                <h1>当前求和为： {this.state.count}</h1>
                <hr />
                <select name="" id="" ref={c => this.selectNumber = c}>
                    <option value="1">1</option>
                    <option value="2">2</option>
                    <option value="3">3</option>
                </select> &nbsp;
                <button onClick={this.increment}>+</button> &nbsp;
                <button onClick={this.decrement}>-</button> &nbsp;
                <button onClick={this.incrementIfOdd}>当前求和为奇数加</button> &nbsp;
                <button onClick={this.incrementAsync}>异步加</button>

            </div>
        )
    }
}
